DIY: Flatten Nested List Iterator

Problem statement

You will be given a nested list of integers named nestedList. Each element will either be an integer or a list whose elements may also be integers or other lists. Your task will be to implement an iterator to flatten the nested list.

You will have to implement the NestedIterator class. This class has the following functions:

• NestedIterator(List<NestedInteger> nestedList), which will initialize the iterator with the nested list nestedList.
• int next(), which will return the next integer in the nested list.
• boolean hasNext(), which will return true if there are still some integers in the nested list and, otherwise, will return false.

You will be given a class definition for NestedInteger and some helper functions. Make sure to look at them in the NestedInteger.java file, in the exercise given below.